1. Field of the Invention
This invention relates to a curing composition which comprises an oxyalkylene polymer having a silicon atom-containing group which has a hydroxyl group or a hydrolyzable group bound to a silicon atom and is capable of crosslinking by forming a siloxane bond. The silicon-atom containing group will be simply called a reactive silicon group hereinafter.
2. Prior Art
An oxyalkylene polymer having a reactive silicon group is curable at room temperature to thereby give a rubber-like material, similar to a room temperature curing silicone rubber. The cured material thus obtained is excellent in tensile properties and adhesiveness and thus is widely available in, for example, sealants and adhesives.
One of the characteristics of an oxyalkylene polymer having a reactive silicon group is that almost every common coating can be applied onto the surface of the material obtained by curing said oxyalkylene polymer. In contrast thereto, no coating can be applied onto the surface of a silicone rubber in practice, since said surface is water- and oil-repellant.
However it is observed that an alkyd coating film formed on the surface of a cured material of a composition comprising an oxyalkylene polymer having a reactive silicon group shows sometimes poor drying characteristics, which can make it impractical to apply said coating onto said cured material.
It was not known why the alkyd coating shows such poor drying characteristics. As the result of our extensive studies, we have found that a plasticizer, in particular, one having a low viscosity and a low molecular weight contained in a curing composition comprising an oxyalkylene polymer having a reactive silicon group deteriorates the drying characteristics of an alkyd coating.
A plasticizer is employed in order to lower the viscosity of the composition to thereby improve its workability or to improve the tensile properties of the cured material.
We have attempted to determine a plasticizer which would not deteriorate the drying characteristics of an alkyd coating. As a result, we have found that the above problem can be solved by using a so-called polymeric plasticizer. We have already filed U.S. patent applications (Ser. Nos. 07/288,177 and 07,290,331 entitled "Method of Applying Alkyd Paints to Oxyalkylene Polymers Having a Reactive Silicone Group" and "Curing Composition of Oxyalkylene Polymer", filed on Dec. 26, 1987 and Dec. 28, 1987, respectively) directed to this discovery.
We have attempted to further improve the drying characteristics of an alkyd coating and consequently found that the drying characteristics of an alkyd coating can be . further improved by using a composition which comprises an oxyalkylene polymer having a reactive functional silicon group and a polymeric plasticizer, thus completing the present invention.